23. Development and Validation of Data Processing Techniques for Aircraft Ground Vibration Testing

The modal identification of large and dynamically complex structures (e.g. aircrafts) often requires a multiple-input excitation. Sine sweep excitation runs are applied in order to concentrate more energy on each line of the frequency spectrum. The work is aimed at developing a new data processing technique for aircrafts Ground Vibration Testing when a multi-point sine sweep excitation is used. The Virtual Driving Point method cancels out the necessity of performing as many sweeps as shakers in order to compute the system’s FRFs. Each single sweep can be individually performed and the measured data can be independently analyzed. As a result, modal analysis is more easily carried out and each single sweep leads to different modes, whose symmetric or antisymmetric nature depends on the relative phase between inputs that has been adopted during that run (mainly 0^∘ and 180^∘). This procedure allows to obtain more defined mode shapes and, more generally, reliable results in terms of modal parameters. New data processing techniques, as the ones object of this work, always require to be validated through their application to different data sets. It is indeed important, in order to asses the reliability of the method, to analyze and compare its outcome when applied to different data and to find a constant improvement with respect to results provided by conventional methods. For this reasons, different GVT measurements were performed and post-processed to validate the proposed approach. Before applying the method to a physically acquired data set, it has been tested on a numerically simulated three DOFs system in order to identify the possible results to which it could lead and the advantages that it could bring. Then, three GVT data sets, during which a two points excitation has been used, have been analyzed: a data set acquired during a measurement campaign on an airplane mockup; a data set related to a scaled airplane model, the Garteur model, which is bigger than the previous one and is characterized, like large aircrafts, by close modes; a data set acquired during a measurement campaign on a real aircraft, the eFusion Magnus electric aircraft developed in cooperation with Siemens.